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4th International Conference on Multiscale materials Modeling, MMM 2008

作者： Vaughan, Ted McCarthy, Conor Composites Research Centre Materials and Surface Science Institute Dept. of Mechanical and Aeronautical Engineering University of Limerick Ireland

ISBN: (纸本)9780615247816

The non-uniform spatial arrangement of fibers in composite materials leads to an irregular stress distribution in the microstructure allowing localized microscopic damage mechanisms to occur more easily. In order to accurately predict such damage mechanisms, statistically equivalent representative volume elements (SERVE) are often used. A hard-core random model, where fibers are randomly placed, is generally used to create these SERVE's but such models do not reproduce the microstructure well for high volume fraction composites, such as those used for high strength applications in the aerospace industry. In this paper, a novel method is developed to generate SERVE's for high volume fraction composites. This method uses experimentally measured nearest neighbor distribution functions to define inter-fiber distances. The resulting SERVE is found to show very similar geometric distribution functions (i.e. radial distribution and nearest neighbor distribution) to the actual microstructure. The proposed algorithm is currently being used to generate micromechanical finite element models for multi-scale damage prediction of composite structures. © MMM 2008. All rights reserved.

关键词： Distribution functions

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Grain growth behaviour and consolddation of ball milled nanocrystalline iron-chromium alloys

Grain growth behaviour and consolddation of ball milled nano...

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TMS 2008 Annual Meeting Supplemental: materials Processing and Properties

作者： Gupta, Rajeev Kr. Raman, R. K. Singh Koch, Carl C. Dept. of Mechanical Engineering Monash University VIC 3800 Australia Dept. of Materials Science and Engineering North Carolina State University Raleigh NC 27695-7907 United States

ISBN: (纸本)9780873397162

Nanocrystalline iron-chromium alloys may provide considerable corrosion resistance, even at low chromium contents. However, processing of such alloys could be a challenge. This paper describes successful synthesis of nanocrystalline Fe-Cr alloys by ball-milling route. In the absence of suitable hot compaction facility, the alloy powder could be successfully compacted close to the desired density, by employing a step of prior annealing of the powder followed by compaction at a relatively low temperature. Grain growth behaviour of Fe-Cr nanocrystalline alloys was investigated at 500, 600 and 700C At 500C, no appreciable grain growth was observed, after the initial period. However, a sudden and rapid grain growth was observed after 90 minutes at 600C, and after 30 minutes at 700C The paper also describes the success in the processing of the nanocrystalline iron-chromium alloys.

关键词： Iron alloys

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Nanotechnology in total joint arthroplasty

Nanotechnology in total joint arthroplasty

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8th World Biomaterials Congress 2008, WBC 2008

作者： Hill, Janet Dunne, Nicholas Orr, John Wang, Dongyan Giannelis, Emmanuel School of Mechanical and Aerospace Engineering Queen's University Belfast United Kingdom Dept. Materials Science and Engineering Cornell University Ithaca United States

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Numerical investigation to examine the effect of introducing a crack in a residual stress field

Numerical investigation to examine the effect of introducing...

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ASME 2008 Pressure Vessels and Piping Conference, PVP2008

作者： Kamel, Simon O'Dowd, Noel P. Nikbin, Kamran M. Dept. of Mechanical Engineering Imperial College London South Kensington Campus London SW7 2AZ United Kingdom Dept. of Mechanical and Aeronautical Engineering Materials and Surface Science Institute University of Limerick Limerick Ireland

ISBN: (纸本)9780791848296

This paper presents a detailed two dimensional finiteelement study to examine the effect of introducing a crack either progressively or instantaneously into a residual stress field. A progressive crack is defined as a crack which is introduced in fixed increments of crack extension until the desired crack length is achieved. An instantaneous crack is one in which a crack of the required length is introduced instantaneously into the finite-element mesh. Inspection is made of the crack tip fields and the crack opening displacements. A modified definition of the J-integral, which accounts for the initial plastic strain due to residual stress, is assessed, in order to examine its ability to characterize the intensity of the near crack tip fields. The implications of the results on fracture assessment of structural components are discussed.

关键词： Residual stresses

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Experimental characterization of florida manatee skin using unconfined compression tests

Experimental characterization of florida manatee skin using ...

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11th International Congress and Exhibition on Experimental and Applied Mechanics 2008

作者： Jagdale, Vijay Clifton, Kari B Mecholsky, John J Howell, Elizabeth A Ifju, Peter Graduate Student University of Florida Dept. of Mechanical and Aerospace Engineering P.O Box 116250 Gainesville FL 32611-6300 United States Postdoctoral Department Mayo Clinic College of Medicine Endocrine Research Unit United States University of Florida Dept. of Materials Science and Engineering United States Undergraduate Student University of Florida Dept. of Materials Science and Engineering United States University of Florida Dept. of Mechanical and Aerospace Engineering United States

ISBN: (纸本)9781605604152

Manatees, listed as endangered species, are marine mammals that are inhabitants of the Florida coastline as well as some of the natural springs The coexistence of the humans and the manatees in the Florida waterways has contributed to the depletion of the manatee population: collisions between watercraft and the manatees are responsible for 25% of all the manatee deaths In an effort to reduce the speed limits in the manatee populated waterways, some studies have been done earlier at the University of Florida (UF) to characterize the manatee rib bone fracture behavior and its impact load carrying capacity Initial estimates and the parallels between other animal studies indicate that the manatee skin acts as an energy absorption element during an impact The purpose of the present study is to characterize the manatee skin in order to understand its response to compressive loading A Visual Image Correlation (VIC) technique is used for the full-field basis measurement of the deformations and the strains VIC results indicate the necessity to model the manatee skin as a layered solid material or functionally graded material The nature of the stress-strain curve indicates the necessity to model the skin via a hyper-elastic idealization.

关键词： Compression testing

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Friction stir processing of Ti-5111

Friction stir processing of Ti-5111

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materials science and Technology Conference and Exhibition, MS and T'08

作者： Rubal, M. Lippold, J. Juhas, M. Welding Engineering Program Ohio State University Columbus OH United States Dept. of Materials Science and Engineering The Ohio State University Columbus OH United States

ISBN: (纸本)9781605606217

Microstructure evolution during friction stir processing (FSP) of Ti-5111 (Ti-5Al-lSn-lZr-lV-.8Mo) performed both above and below the beta-transus temperature was investigated. Plate samples for FSP were fully instrumented with thermocouples to record the thermal histories experienced within the stir zone and in the adjacent heat-affected zone (HAZ). Temperature profile analysis was performed using single sensor differential thermal analysis (SS-DTA) which allowed determination of the beta transus both during heating and cooling. The FSP microstructures were characterized using optical and scanning electron microscopy. The microtexture of the stir zones were compared to the base material using electron backscatter diffraction (EBSD). Friction stir processing both above and below the beta transus resulted in extreme grain refinement, reducing the 200-500 μ base material grains to 1-20 μ depending on processing temperature. The above-transus stir zone exhibited a transformation texture in the α phase and a deformation texture in the β phase. Both the α and β phase exhibited deformation textures in the sub-transus stir zone. The introduction of extreme deformation during FSP above the beta transus depressed the on-cooling beta transus by more than 100 °C below the equilibrium value. © 2008 MS&T'O8.

关键词： Differential thermal analysis

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Role of micro-/nanocrystalline structure in oxidation of FE-CR alloys

Role of micro-/nanocrystalline structure in oxidation of FE-...

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48th Annual Conference of the Australasian Corrosion Association 2008: Corrosion and Prevention 2008

作者： Singh Raman Rajeev, R.K. Gupta, K. Atanacio, A.J. Prince, K. Koch, C.C. Dept. of Mechanical and Aerospace Engineering Monash University VIC Australia Department of Chemical Engineering Monash University VIC Australia Australian Nuclear Science and Technology Organisation NSW Australia Dept. of Materials Science and Engineering North Carolina State Uni. United States

ISBN: (纸本)9781622762446

A simplistic approach would suggest a greater corrosion rate of an alloy in its nanocrystalline state than in microcrystalline state, due to a larger fraction of grain boundaries (i.e., high energy area) in the former. However, the nature of influence of nanostructure on corrosion does not seem to be similar in all cases. The nature of the influence can be opposite, depending on the type of corrosion and environment-material system. A considerably improved corrosion resistance of an Fe-C alloy in the nanocrystalline state (as opposed that in the microcrystalline state) has been established.

关键词： Corrosion rate

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Numerical simulation and experimental study of manufacturing saddle shape sheet workpiece using multi-point sandwich forming

Numerical simulation and experimental study of manufacturing...

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9th International Conference on Technology of Plasticity, ICTP 2008

作者： Wang, Z.R. Zhang, Q. Teng, B.G. Dean, T.A. Harbin Institute of Technology School of Materials Science and Engineering Harbin 150001 China Dept. of Mechanical and Manufacturing Engineering School of Engineering University of Birmingham Birmingham B15 2TT United Kingdom

ISBN: (纸本)9788957081525

To significantly reduce the time and cost of tooling for sheet metal parts, the multi-point sandwich forming (MPSF), a new reconfigurable die forming technology, is being developed for parts with various curvatures made in small batch quantities. In this paper, the saddle shape, a special kind of double-curved shape with positive and negative curvature, has been chosen as the multi-point die shape to manufacture workpiece. Because the negative curvature regions of saddle workpiece are difficult to form due to flowing limitation of elastic material in upper die, the multi-step forming methods, changing the upper die shape and changing the workpiece position, were put forward to improve the dept. of saddle workpiece. During the deformation of workpiece, bulking maybe occur in the middle of saddle workpiece. The results show that the emergence of bulking is due to the insufficient normal pressure acting on the middle of surface of saddle workpiece and bulking can be depressed by using the reasonable upper die shape.

关键词： Dies

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Using nonlinearity to improve the performance of vibration-Based energy harvesting devices 7

Using nonlinearity to improve the performance of vibration-B...

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7th European Conference on Structural Dynamics, EURODYN 2008

作者： Mann, Brian P. Sims, Neil Mechanical Engineering and Materials Science Duke University Box 90300 DurhamNC 27708 United States Dept. of Mechanical Engineering Sheffield University Mappin Street SheffieldS1 3JD United Kingdom

ISBN: (纸本)9780854328826

This paper investigates the design and analysis of a novel energy harvesting device. The governing equations for the mechanical and electrical domains are derived to show the designed system reduces to the form of a Duffing oscillator under both static and dynamic loads. Theoretical investigations are followed by a series of experimental tests that validate the response predictions. The motivating question for the current work was whether nonlinear phenomenon could be exploited to improve the effectiveness of an energy harvesting device.

关键词： Energy harvesting

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Replications of Critical Technological Processes and the Use of Replicates as Characterization Standards: An Experiment in Undergraduate Education

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MRS Online Proceedings Library 2008年第1期1047卷 4-23页

作者： Pamela B. Vandiver Heather Raftery Stephanie Ratcliffe Brian T. Moskalik Michelle Andaloro Katelyn Sandler Alicia Retamoza Dept. of Materials Science and Engineering Program in Heritage Conservation Science University of Arizona Tucson USA

The technology of artifacts is analyzed and reconstructed by comparison with known craft practices, the physical and chemical constraints imposed by the raw materials, and the sequence and steps for processing those materials to achieve certain optical and mechanical properties. Understanding of craft knowledge is best pursued by practice, coupled with technical analysis. Six case studies of hands-on, undergraduate student laboratory projects are presented. The studies include testing parameters for the making of stenciled hand images similar to those at caves such as Gargas from the Upper Paleolithic period in France, the variation in processing required to produce Egyptian blue pigments and objects, controlling composition to form either green or turquoise-blue colors in Islamic lead-containing glazes, optimizing the ratio of various pigments to gum Arabic medium in tomb paintings to evaluate application and durability, molding East Asian gokok beads in imitation of jade, and making and radiographing a mock-up of a damaged statue on the façade at the San Xavier Mission as a standard for comparison with the original. In each case, various parameters are varied to model the appearance, structure and composition of an object, and the students benefited from the experience of developing research questions and from their involvement in original research projects.

关键词： archaeology ceramic sintering

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